1 Technical Field of the Invention
The present invention relates generally to a motor-generator suitable for use in vehicle such as passenger cars or trucks, and more particularly to an improved structure of such a motor-generator which have improved electrical and mechanical responses without sacrificing the performance thereof.
2 Background Art
Recently, it has become essential to reduce mechanical shocks caused by application of engine torque to auxiliary parts or engagement of an automatic transmission while the engine is idling so that the engine torque is low. In order to avoid this problem, some of typical automotive motor-generators are designed to be controlled to increase the quantity of power to be generated gradually when an electrical load is applied to the motor-generator suddenly. Additionally, in recent years, a variety of electrical parts such as electrical steering systems which consume a large quantity of power instantaneously and need a higher response and comfort of operation have been employed. The need for releasing the torque of the engine from being consumed by the auxiliary parts instantaneously is, thus, required in order to compensate for a lack of torque of the engine for driving the vehicle. This may be achieved typically by using a motor-generator driven through transistors and controlling a motor torque thereof at high speed through a vector control system.
The above system requires a complex control mechanism and transistors allowing much current to flow therethrough, and thus results in an increase in manufacturing cost. The motor-generator is employed as an electric motor, thus resulting in an increase in mechanical time constant. This requires large-sized transistors and a large capacity of a battery, thus resulting in an increase in load on a charge system. The need for altering the design of the system or using expensive parts may be eliminated by regulating a field current of the motor-generator installed in the vehicle to control the output torque thereof at high speed. The decrease in mechanical time constant may be increasing a field resistance or decreasing the number of turns of a field winding. This, however, results in a drop in degree of excitation of the field winding, which is objectionable in terms of an increase in electrical load.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a motor-generator designed to have an improved electrical response of a magnetic field and an improved mechanical response without sacrificing the performance of the motor-generator.
According to one aspect of the invention, there is provided a motor-generator which is suitable for use in automotive vehicles. The motor-generator comprises: (a) an armature including polyphase windings; (b) a field core; (c) a field winding wound around the field core; (d) a pole rotor disposed between the armature and the field core to be rotatable together with a rotary shaft, the pole rotor being made up of a first inductor core and a second inductor core arrayed adjacent each other in an axial direction of the rotary shaft; and (e) a plurality of permanent magnets arrayed at an interval of 2xcfx80 in electrical angle of the armature away from each other in each of the first and second inductor cores of the pole rotor in a circumferential direction of the first and second inductor cores. Each of the permanent magnets is magnetized in a radius direction of the first and second inductor cores so as to be opposed to a magnetomotive force produced by the field winding, thereby resulting in quick disappearance of the magnetic flux of the field upon disappearance of the magnetomotive force from the field winding, which results in a greatly improved electrical response of the field.
In the preferred mode of the invention, a plurality of slits are formed in each of the first and second inductor cores. Each of the slits extends in the radius direction of the first and second inductor cores and is located between adjacent two of the permanent magnets. The slits may be arrayed at an interval of 2xcfx80 in electrical angle of the armature from each other.
The motor-generator further comprises a housing to which the pole rotor is fixedly attached to form a brushless magnetic circuit. It is advisable that each of the permanent magnets be located closer to the armature than the field core in the radius direction of the first and second inductor cores. This results in an increase in magnetic force acting on the armature. The formation of the brushless magnetic circuit results in an increase in air gap within a main magnetic circuit. The installation of the permanent magnets in the main magnetic circuit results in an increase in magnetic resistance of the main magnetic circuit, which leads to a great decrease in inductance of the main magnetic circuit. Mechanically, a rotating portion is allowed to have a minimum structure including the pole rotor. The magnetic flux passes directly from the field core to the armature, thus permitting the size or weight of the rotating portion to be reduced, which results in an improved mechanical response thereof. The presence of the permanent magnets in the vicinity of the armature results in improved permeability of the magnetic flux from the field core to the pole rotor, thereby permitting the pole rotor to be reduced in size, which results in further improvement of the mechanical response.
The field core is made up of a boss around which the field winding is wound and discs attached to ends of the boss opposed to each other in the axial direction of the rotary shaft. Hollow cylinders are further provided which are disposed on peripheries of the discs, respectively, and each of which has a length greater than a thickness of the discs in the axial direction of the rotary shaft. Each of the discs extends radially from peripheral edges of the boss to define a gap within which the field winding is installed. Each of the hollow cylinders extends over the gap close to each other through a given interval, thereby resulting in improved permeability of the magnetic flux flowing from the discs to the first and second inductor cores, which allows the pole rotor to be reduced in size, thereby resulting in a decrease in mechanical inertia.
The AC motor-generator further comprises a second permanent magnet which is disposed between the first and second inductor cores of the pole rotor. The second permanent magnet is magnetized so as to be opposed to the magnetomotive force produced by the field winding, thereby avoiding leakage of magnetic flux to between the first and second inductor cores and adding the magnetic flux produced by the second permanent magnet to the armature as the magnetic flux of the field, which improves an output of the AC motor-generator or allows the pole rotor to be reduced in size if the output of the AC motor-generator is kept constant, thus resulting in a decrease in mechanical inertia.
The AC motor-generator further comprises a magnetic flux leakage deterrent permanent magnet disposed between the field winding and the pole rotor which is so magnetized as to decrease a leakage of magnetic flux into between the discs of the field core. The magnetic flux leakage deterrent permanent magnet also works to add the magnetic flux produced thereby to the armature as the magnetic flux of the field, which improves an, output of the AC motor-generator or allows the pole rotor to be reduced in size if the output of the AC motor-generator is kept constant, thus resulting in a decrease in mechanical inertia.
The AC motor-generator further comprises a control circuit which works to energize the field winding and change a direction in which the field winding is energized. Even when the field winding is not energized, the permanent magnets continue to produce the magnetic flux, so that a small amount of power is being generated. The control circuit works to suppress the generation of power.